Sand screen



March 16, 1965 R. F. RENSVOLD SAND SCREEN Filed Dec. 26. 1961 IOa FIG. 3

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INVENTOR.

Roger E Rensvold BY W, W l

United States Patent 3,173,488 SAND SCREEN Roger F. Rensvold, Duncan, Okla, assignor to Halliburton Company, Duncan, Okla, a corporation of Delaware Filed Dec. 26, 1961, Ser. No. 161,925 Claims. (Cl. 166-228) The present invention relates to a new and improved sand screen and to a method of manufacturing said screen.

The present invention particularly relates to a preformed downhole device adapted to control sand produced from unconsolidated formations in flowing or pumping oil wells and water wells.

Prior art sand screens, of the type which this invention improves upon, consist essentially of an outer cylinder of sand bonded together and held in place by a thermosetting resin around standard slotted tubing, which permits the screening action to be diffused over the screens entire surface. The sand grains used in screens of this type are preferably uniform and a round Ottawa sand of 20-40 mesh has been found to be suitable for most formations. Special gradations of sand may be used for particular formations as desired or required.

One of the disadvantages of such prior art sand screens is that in the manufacture of these screens, sand easily becomes lodged in the slots in the tubing. This reduces the total area of the tubing slots available for fluid production through the screen and thereby renders the screen less effective.

The present invention and the manufacture thereof are particularly adapted to overcome the above disadvantage.

An important object of the present invention is to provide a new and improved sand screen which has a significantly higher flow rate at a given differential pressure than conventional or prior art sand screens.

Another important object of the present invention is to provide a new and improved method of manufacturing or making a pre-formed sand screen of the resin-bondedsand type.

. The construction and method designed to carry out the invention will be hereinafter described, together with other features thereof.

, The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a partthereof,[wherein an example of the invention is shown, and wherein:

FIG. 1 is a view partly in elevation and partly in section illustrating the slotted tubing or mandrel of the present invention prior to the sand being bonded thereto;

FIG. 2 is a sectional view of the mandrel of FIG. 1 after the initial coating of sand has been bonded thereon.

FIG. 3 is a view partly in section and partly in elevation of the device of the present invention after the second layer of sand has been bonded thereto; and

FIG. 4 is an enlarged view of a portion of the mandrel and first sand coating as shown in FIG. 2.

The well screening device or sand screen of the present invention includes a tubing member or mandrel having a plurality of openings or slots 11 therein. In the preferred form of the invention, these slots 11 extend longitudinally around the mandrel 10 and in a pattern as illustrated in the drawings. The mandrel 10, as illustrated, is a section of standard slotted tubing well known in the art. Any other suitable types of openings and/or arrangements thereof may be used without departing from the scope of the invention.

A layer 12 of sand grains 13 which are bonded on the mandrel 10 and together with each other by a thermosetting resin or other suitable bonding agent is formed around the mandrel 10. This initial layer 12 of sand grains 13 preferably extends substantially the length of 3,173,488 Patented Mar. 16, 1965 ice the mandrel 10, but may cover as much or as little 'of the mandrel 10 as desired. The sand grains are sufliciently large that they cannot enter into or lodge in the slots or openings 11 of the mandrel 10. A San Saba sand of from about 8 to about 12 mesh has been found particularly desirable for the initial layer with a slot width of .050 inch. The size of the sand grains 13 may be varied with the size of the slots 11. An illustration of the relationship between the slots 11 and the sand grains 13 may be more clearly seen in FIG. 4.

A second layer 14 of sand grains 15 is bonded on and around the layer 12. The grains 15 are smaller than the grains 13 and normally would be small enough to pass through or lodge in the opening 11 of the mandrel 10. This second layer 14 may be as many grains thick as desired, depending upon the size well hole the screen is to be positioned therein and the size of the mandrel 10. Ottawa sand of from about 20 to about 40 mesh has been found to be very effective for most formations and gives a good screening action which is diffused over the entire surface 16 of the screen S.

The type of formation in which the sand screen S is to be positioned will normally dictate the mesh size of the sand grains 15 of the second layer 14, and as stated hereinabove, a mesh size of about 20 to about 40 has been found suitable for most formations. The size of the sand grains 15 of the layer 14, together with the size of the slots 11, will determine the most desirable size of the sand grains 13 of the layer 12.

It is well known in the art, that the primary screening layer must be composed of adequately small or fine grains of sand to effectively screen the fluids produced therethrough. It is also well known in the art, that the slots in the mandrel must be sufficiently large that a suitable amount of fluid may be produced therethrough. It is generally found that the most desired size of sand grain is sufiic ently small to enter or lodge in the most desired size slot. The importance of this invention can therefore be readily seen, as the present invention enables the most desired layer of sand to be chosen without the necessity of reducing the size of the slots in the mandrel or tubing.

The mandrel 10, as illustrated in the drawings, has external upset ends 10a and 16b which have suitable threads 10c and 10d, respectively, thereon for facilitating the positioning of the screen S in a well string. Other types of connecting mediums may be employed as desired.

One end 10b of the mandrel 10 is fitted with lugs 17 which may be welded thereto or aflixed thereon by any suitable means. A centralizer 18 is mounted on the lugs 17. The centralizer 18 is of a diameter approximating that of the well bore in which the screen S is to be positioned therein. The centralizer 18 protects the screen S from being damaged as it is lowered into the well bore in a manner well known in the art. The sand screen S may be used with or without a centralizer, and various types of centralizers may also be used, all within the scope of the present invention. Other accessories such as anchor shoes and tension sleeves may also be added to the sand screen S of the present invention as desired or needed.

A tubing collar 19 is connected to the end 1012 of the mandrel 10 and retains the centralizer 18 on the screen S in the desired position. The collar 19 also enables the screen S to be connected in the well string or to other screens or tools as desired.

The sand screen S may be of any desired length or width as particular well conditions may required. A screen S having an overall length of six (6) feet has been found to be particularly desirable. As these screens are pre-formed, it is preferred that that they be manufactured of standard lengths. Several screens may be joined together as desired for long producing intervals.

Flow Area Opening, Square Inches Flow Area Tube, Square Inches Surface Area, Square Inches Mandrcl Size Screen Casing Size 5 Size tom It should be noted that these examples are solely for illustrative purposes and in no ways intended to limit the invention. Other sizes and gradations may be made for particular conditions and as desired.

The device S of the present invention is prepared or manufactured by first cutting the mandrel to the prescribed length, threading the ends thereof and placing the openings or slots 11 therein, all in a manner well known in the art.

In preparing the mandrel 10 for being coated with sand, it is preferable that the mandrel be clean. This may best be accomplished by sand blasting the mandrel 10.

After the mandrel 10 is sand blasted, it is first coated with a catalyzed epoxy resin. When the tacky stage is reached, the tubing 10 is rolled in a bed of coarse, resin-coated sand, which forms a layer 12 one sand grain 13 thick on the tubing. These sand grains 13 are of a size that they cannot lodge in or plug the slots 11. This resin-sand layer 12 around the mandrel 19 is then allowed to cure.

The smaller sand grains are coated with a similar catalyzed epoxy resin and then bonded on the layer 12 3 to form the layer 14 in the desired or predetermined thickness.

An illustration of preparing or making the sand screen S of the present invention and a prior art sand screen is as follows:

Two 2 /8" O.D. x 72".EUE slotted mandrels were sand blasted and used to form the mandrel of each sand screen. Each of the mandrels was slotted in an similar manner wherein the slots were .050 inch in width and 2.0 inches in length.

The first mandrel was painted with a resin having the following formula:

, Parts Epon 828 (trade name of an epoxy resin made by Shell Chemical Corp. This resin is a homolog of diglycidyl ether of bisphenol A. It is a liquid at room temperature, has an epoxide equivalent of from 175 to 210, an average molecular weight of 350 to 400, and a viscosity of from 5,000 to 15,000 centipoises at 25 centigrade.) Catalyst Z (trade name of a curing agent for Epon 828 and is also made by Shell Chemical Corp. It

is a modified, aromatic polyamine) SR-32 (tradename of a silicone resin made by General Electric Silicone Products Department and used as a levelling agent) Cab-O-Sil (registered trademark of Cabot Corp, Boston, Mass, for fumed silicon dioxide as a free flowing or anticaking agent) The resin was applied on the mandrel with a 2 paint brush, stroking the surface vigorously so that a film of resin as thin as possible commensurate with its viscosity is left thereon.

This coated first mandrel was then placed in a base holder and three sections of 5%" sand screen mold was fastened around it. A quantity of loose, dry, 8-12 mesh, San Saba sand was poured into the annulus, completely surrounding the resin-wet mandrel. The mold sections were rapped sharply with a hammer thereby assisting the compaction of the loose sand. 7

The entire mold assembly was placed in an oven, where the resin was cured for 2 /2 hours at 350 F. At the end of this period, the mold assembly was removed from the oven, the loose sand poured out, and the sandcoated mandrel allowed to cool to room temperature. The mandrel was then at the stage as illustrated in FIG.

2 of the drawings.

The second mandrel was coated with a resinous mix ture of Epon 828 and Genamid 250. (Trade name of a ruling agent and coreacting resin made by General Mills Co. It is a condensation polymer of vegetable oil, unsaturated fatty acids, and aryl or alkyl polyamines.) After the coating became tacky, the mandrel was placed in the 3.9" mold and resin-wet 2040 mesh Ottawa sand was tamped into the annulus in the normal manner.

The first mandrel, which had been pre-coated, was likewise placed in a 3.9" sand screen mold and resin-wet 20-40 mesh Ottawa sand was tamped into the annulus.

Each of the mold assemblies was then placed in an oven and cured for three hours at 350 F. After such curing period, the sand screens were removed from the molds and allowed to cool to room temperature.

Airflow tests and water flow test were then made on each screen, measuring flow rates and differential pressures. The results of these tests were as follows:

Air flow test Air Flow, Percent Differential Pressure, p.s.i.

Second Screen First Screen (Conventional) (Pre-Coatcd) Water Flow Test NORMAL FLOW FLOW Psi-pounds per square inch. P.s.i.g.pounds per square inch gauge. G.p.rn.gallons per minute.

It can readily be seen from the above comparative resuits that the performance of the sand screen of the present invention or pre-coated sand screen is significantly better than that of the conventional sand screen.

The sand screens of the present invention are also much easier to backfiush than the prior art type sand screens.

It should be noted that the resin formulation hereinabove was found to be particularly suitable for the present invention. Any other suitable resin formulation or bonding agent may be used without departing from the scope of the present invention.

The epoxy resin and catalyst may be used without the other additives if desired and are thoroughly blended before being used. The additives such as the fumed silicon dioxide are preferably added after such blending. The silicon dioxide results in a resin mix of an increased or higher viscosity, which in turn results in a thicker layer of resin on the mandrel or pipe. This enables a better Wetting of the sand grains contacting the pipe surface during the curing process and thus a better coating or layer of sand grains around the pipe or mandrel.

The resin-coated sand used in the preparation of the sand screen S is normally prepared by first mixing and thoroughly blending the resin and catalyst. Although the invention has been illustrated using an epoxy type resin, any other thermosetting resin or other suitable bonding agent may be used without departing from the scope of the invention.

Should any additives be desired, they are normally added after the initial blending of the resin and catalyst and then thoroughly mixed therewith. After the resin is thus blended, the sand is added and the resin thoroughly mixed or blended therewith. The more uniform the coating of the sand grains, the more uniform will be their position bonded around the mandrel.

In carrying out the process of the present invention, it is possible that the first layer of the coarser or larger sand grains will not be uniformly exactly one sand grain in thickness, however, the layer will be substantially one grain in thickness.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction and method, may be made within the scope of the appended claims without departing from the present invention.

Broadly, the invention relates to a new and improved sand screen and a method of making same.

What is claimed is:

1. A well screen device adapted to be positioned in a well bore for controlling sand produced from unconsolidated formations, comprising:

a mandrel having a plurality of openings therein;

a substantially uniform initial layer of sand bonded on said mandrel,

said initial layer of sand being substantially one sand grain in thickness,

each of said sand grains of said initial layer of sand being sufficiently larger than said openings in said mandrel that the lodging of said sand grains in said openings is substantially prohibited; and,

a second layer of sand bonded together and on said initial layer of sand,

the grains of sand of said second layer being smaller than the grains of sand of said initial layer.

2. The structure recited in claim 1, wherein;

the sand of said first layer consists essentially of sand grains of about 8 to about 12 mesh said sand of said second layer consists essentially of sand grains of about 20 to 40 mesh and,

the openings in said mandrel being sufficiently large to pass sand grains of about 20 to about 40 mesh.

3. The structure recited in claim 1, wherein:

the openings in said mandrel are a plurality of longitudinally and spaced apart slots,

the width of said slots being sufficiently smaller than the sand grains of said initial layer that said sand grains are prohibited from lodging therein.

4. In a well screen device adapted to be positioned in a well bore:

a mandrel having a plurality of slots therein;

a first layer of sand grains of sulficient size as to be prohibited from entering the slots in said mandrel substantially one sand grain in thickness bonded on said mandrel; and

a second layer of said grains smaller than said sand grains of said first layer of a predetermined thickness for providing a fluid screen bonded on said first layer of sand grains.

5. In a sand screen adapted to be positioned in a Well bore for controlling sand produced from unconsolidated positions:

a mandrel having a plurality of spaced apart slots systematically arranged thereon and having a predetermined total flow area;

a first coating of sand grains sufficiently larger than the width of said slots so as to be prohibited from lodging therein,

said sand grains being bonded on said mandrel by a catalyzed epoxy resin; and

a subsequent plurality of coating of sand grains smaller than the sand grains of said first coating,

said sand grains of said subsequent coatings being pre-coated with a catalyzed epoxy resin and bonded on said first layer of said grains and to each other by said resin.

Rererences Cited by the Examiner UNITED STATES PATENTS 1,992,718 2/35 Records 166-230 X 2,730,769 1/ 5 6 Isenberg 18-59 2,747,230 5/56 Magnus 1859 2,843,209 7/58 Degen 166--228 3,039,535 6/62 Hathorn et al. 1 66-228 CHARLES E. OCONNELL, Primary Examiner.

NORMAN YUDKOFF, Examiner. 

1. A WELL SCREEN DEVICE ADAPTED TO BE POSITIONED IN A WELL BORE FOR CONTROLLING SAND PRODUCED FROM UNCONSOLIDATED FORMATIONS, COMPRISING: A MANDREL HAVING UNIFORM INITIAL LAYER OF SAND BONDED A SUBSTANTIAL UNIFORM INITIAL LAYER OF SAND BONDED ON SAID MANDREL, SAID INITIAL LAYER OF SAND BEING SUBSTANTIALLY ONE SAND GRAIN IN THICKNESS, EACH OF SAID SAND GRAINS OF SAID INITIAL LAYER OF SAND BEING SUFFICIENTLY LARGER THAN SAID OPENINGS IN SAID MANDREL THAT THE LODGING OF SAID SAND GRAINS IN SAID OPENINGS IS SUBSTANTIALLY PROHIBITED; AND A SECOND LAYER OF SAND BONDED TOGETHER AND ON SAID INITIAL LAYER OF SAND, THE GRAINS OF SAND OF SAID SECOND LAYER BEING SMALLER THAN THE GRAINS OF SAND OF SAID INITIAL LAYER. 